1. Field of the Invention
The present invention relates to a process for preparing 4-substituted-5-pyrazolones from 3-alkylamino-5-pyrazolones, 3-arylamino-5-pyrazolones or 3-N-heterocyclic (substituted) amino-5-pyrazolones as starting materials.
2. Description of the Prior Art
It is well known that 5-pyrazolones are important compounds as magenta couplers in the field of photography and that they are useful materials as intermediates for synthesizing medicines or dyestuffs. For example, in the field of photography, when conventional silver halide emulsion type color photographic sensitive materials containing 5-pyrazolones are subjected to color development after exposure to light, the 5-pyrazolones function as couplers and form corresponding azomethine dyes by oxidative coupling with p-phenylenediamine type color developing agents to form magenta images.
It is also well known that 4-unsubsituted-5-pyrazolone couplers stoichiometrically require 4-equivalents of silver halide as an oxidizing agent, because one molecule of the coupler forms one molecule of azomethine dye by an oxidative coupling reaction. On the contrary, 5-pyrazolones having a substituent at the 4-position which is easily released at coupling stoichiometrically require only 2 equivalents of silver halide for forming dyes. Various kinds of releasable groups on the 4-position of such pyrazolone couplers are known. They are, for example, described in U.S. Pat. Nos. 3,253,924, 3,311,476, 3,419,391, 3,522,051 and 2,434,272. Pyrazolone couplers which exhibit a development inhibiting effect around the periphery of the image areas due to the interaction of a group released at coupling with silver halide adjacent to this group are also known. Namely, these kinds of 4-substituted 5-pyrazolones are 2-equivalent couplers which release a development inhibitor (DIR Coupler), and are described in, for example, U.S. Pat. Nos. 3,227,554, 3,701,783, 3,148,062, 3,617,291 and 3,006,759.
Further, 3-alkylamino-5-pyrazolone type couplers, 3-arylamino-5-pyrazolone type couplers and 3-N-heterocyclic amino 5-pyrazolone type couplers have excellent color forming properties, excellent color fastness and excellent color hue (for example, as described in U.S. Pat. No. 2,311,081 (U.S. Reissue Pat. No. 22,329)).
It is understood from the above descriptions that 3-N-substituted amino-5-pyrazolones having a releasable substituent at the 4-position are very important compounds in the preparation of color photographic sensitive materials.
Processes for preparing 4-substituted-5-pyrazolones can be classified into two types, that is, a process which comprises introducing a substituent into the 4-position of the pyrazolone ring after formation of the pyrazolone skeleton and a process which comprises previously introducing a substituent into a position corresponding to the 4-position of the pyrazolone ring and then forming the pyrazolone skeleton. Comparatively few examples of the latter process, which is described in British Pat. No. 1,284,649 and Japanese Patent Publication (OPI) No. 100057/75, are known. On the contrary, many examples concerning the former process wherein a substituent is introduced into the 4-position of the pyrazolone ring after formation of the 5-pyrazolone skeleton, which are described in, for example, U.S. Pat. Nos. 2,434,272, 3,148,062, 3,006,759, 3,522,051, 3,227,554, 3,701,783, 3,617,291, 3,311,476 and 3,419,391 and Japanese Patent Publication (OPI) No. 53372/75, are known.
Almost all of the above-described processes in which a substituent is introduced into the 4-position after formation of the pyrazolonering are not suitable, because there are restrictions on the preparation or on the structure of the compound. Namely, the desired compounds are obtained in a low yield because of long complicated steps and of the use of 4-amino-5-pyrazolones or 4-hydroxy-5-pyrazolones as starting materials or the desired compounds are prepared using complicated processings carried out after azo-coupling with 5-pyrazolones. Further, a linking group is limited to a sulfur or selenium containing group through an arylthio, alkylthio or heterocyclic thio group can be introduced directly to the 4-position of 5-pyrazolones by means of sulfenyl chloride.